Warning agent and process for the odorization of a hydrocarbon fuel gas therewith



United States Patent WARNING AGENT AND PROCESS FOR THE ODORIZATIONOF A HYDROCARBON FUEL GAS THEREWITH John vS. McClure, :San Rafael, Califi, assignor to California Research Corporation, San Francisco, Califi, a corporation of Delaware No::Drawing. Application March 7, 1955 se fit No.-; 4 1, 97

10 Claims. (Cl. 4s,- 195 The present invention relates toimixtures of organic sulf ur compounds suitable for the odorization of combustible jhydroc arbon gases, such as natural gas, vapors and gases recoverable inthe refining of petroleum, and other gases suitable as fuels for heating, illuminating and cooking purposes.

More particularly, the invention is directed: to combustible gases suitable as fuels for heating,.illuminatingrand cooking uses, and ordinarily having no .marked inherent odor, which contain vaporizedtherein asmall quantity of a mixture of organic sulfur compoundsposses sing a specificand persistent odor serving} torwarn, of the,scape of the cqmbustiblegas from containers, transmission lines or fixtures and, consequently, serving to warn ofrthe danger of explosion and asphyxiation.

A satisfactory odorant for combustible gases,vs,uch as natural gas,.us ed in the home or in the industrylfor cooking hea'ting or illumination, must comply with the ffollowag requirements: (1) it must possess a distinctive odor to impart a timely warning of the escaping gas, even though initially presentin smallponcentrationin the ambient air; (2) 'the o dorant must not, however be so ofiensive that the users ofthe combustible. gas would object toitspresence in the gas and it mustbevo dorless when burned; (3) furthermore, the odorant m ust be of such a character, and must be used" in such amounts, that -it-would not cause any objectionable skin irritation, lachryrnation, or otherharniful physiological efiects. Another desirable property in an odorant is the gradual cumulation of the intensity 9f the odor so as to render unlikely olfactory fatigue to 'those who happen to be exposed-tothecontinuouslytescaping gas.

- Whileinthe-past, eflortsof-thdse engaged in the odorant art -have been directed toward the discovery ofan ideal materialacombiningihe-several aforementioned desiderata, SO i far I the odorants offered-to the trade havefallen -far short ofthe :desired goal. ulndividual aliphatic C -C \mercaptans. and t mixtures thereof, although they exert an tadeq-ua'te impact on the unwary,gas user, are not sufii- ;cientlyt stable aandotendato become oxidized. Olfactory "ifatigue is another deficiency ofumercaptans. :Theirodor is: of an tofiensive, garlicky or oniony character and their presence in the combustible-gas--tends--topromote corrosion -of themetal appliances,particularly burners and pilots. "On the other hand, odorants of the cyclicsulfide Ltype, such as tetrahydrothiophene, while 'stable'to oxidations and non-corrosive I toinetal equipment when in use, tlagtbehind the mercaptan-typeaodorant with respect to the sodoraintensity and Ethe initial impact on the olfactory .sense.

Alprincipal .object-sofrthe present invention is the. prep- 2,823,104 Pat nted Feb. 11, 1958 ICE dialkyl monosulfides. A mixture. of this kind usually comprises at least two ditferentsdialkyl monosulfidesin which the alkyl radicals are C C; alkylradicals. ,Eachdialkyl sulfidewhich forms apart of the composition of thew arning agent of the invention must bepresent therein ,in an amounpequalifrom at least 10% up to as -high ,as

of the total volume of dialkyl monosulfides"; preferably it should be present in, an amount iequal'to at le ast ,2 Q%

of this volume. .When only two dialkyl sulfides are present in the odorant mixture, the secondsulfide .will i be ,prese nt inan amount substantially equalto theiba la nce to make up by volumeofthe total mixture. If

moreth an two dialkyl sulfides enterthe compositioirof the odo rant, eachpf these sulfidesshould be presenttherein in an amount equal to at least 10%, andVpre ferably at least 20%, by volume of the total sulfide mixture, the. sum

of,the volumessof all sulfides adding up to 100%.

Among the dialkyl sulfides which maybe present in the od orants or. warning agents -in combinations ofpfwo or more the following may be mentioned:

Dimethyl sulfide Diethyl sulfide Dipropyl sulfide D s opy Sul Dibutyl sulfide Di-(Z-methyl propyl)-sulfide -Di-(.1-methyl propyl)-sulfide Methyl ethyl sulfide .Methyl n-propyl sulfide .,Methyl isopropyl sulfide gMethyl n-butylsulfide H Methyl- (2vmethyl propyl) -sulfide lMethyl-( l-methyl. propyl) -sulfide Ethyl n-propyl sulfide Ethyl isopropyl sulfide Ethyl nrhutyl sulfide i-Ethyl- (2-methyl propyl) .-sulfide Ethyl-( l-methyl propyl) -sulfide rn-Pr opyl n-butyl sulfide Isopropyl n-butylsulfide n-Propyl-(Z-rnethyl propyl) -sulfide nPropyll-methyl propyl) .-sulfide Isopropyl- (2- 1nethyl propyl) Tsulfide lsopropyl-( l-methyl propyl)-sulfide .n-Butyl-(Z-methyl V propyl)-sulfide .n-Butyl-( 1-methyl propyl)-sulfide YZ-Methylpropyl-( l-methyl propyl) V-sulfide n-Propyl isopropylsulfide Those C C difllkyl sulfides, inswhich the sum of c ar bonatoms in the two alkyl groups does not exceed 6. are preferred, because of their higher volatility, a valuable characteristic in view of the pressures employed intransmitting odorized fuel gases through the lines from -the source to the consumer, and, furthermore, in view of the fluctuations of temperature during the colder seasons;

Effectiveswarning agents are provided by two-component. mixtures of dialkyl sulfides in which the C 0 alkyl groups of one of the sulfides are identical (RSR),,as in groups of the second sulfide are different (R SR e. g., ethyl isopropyl sulfide, methyl n-butyl sulfide, ethyl npropyl sulfide, and the like.

The aforementioned dialkyl monosulfide mixtures may be prepared in any suitable manner and can be introduced into containers, tanks, or transmission lines containing combustible hydrocarbon gas in accordance with the conventional odorization techniques (described, e. g., in American Gas Association Proceedings for 1950, at pages 684 to 694). Amounts ranging from 0.5 to 2.0 pounds per one million cubic feet of gas will assure effective odorization thereof.

Dialkyl sulfide mixtures particularly effective as odorant or warning agent components of combustible hydrocarbon gases according to the present invention can be prepared by dissolving one or more lower molecular weight C -C aliphatic mercaptans in a solution of a strong alkali, e. g., 20% caustic, heating to a temperature from about 175 to about 300 F. under a pressure which may range from 30 to 160 p. s. i. g., and reacting the resulting mercaptide solution with a C -C alkyl chloride, or a mixture of C -C alkyl chlorides, so as to yield upon cooling, settling, drawing of water, and if necessary distilling, a reaction product in which the dialkyl sulfides are present in amounts equal to at least 10% each, and preferably in amounts equal to at least 20% by volume, based on the total volume of the final product.

In a typical illustration of the odorization of combustible hydrocarbon gases in accordance with the invention, the odorant, or warning agent, is prepared by dissolving isopropyl mercaptan and ethyl mercaptan (in a volume ratio of 2 to 1) in an aqueous solution of 20% caustic. The resulting solution is contacted with ethyl chloride at a temperature of about 250 F. and under a pressure of approximately 60-65 pounds. The reaction may be expressed by the following equation:

(1.0 mol) (0.4 mol) (0.6 mol) (1.0 mol) Cam-s Cam -Ca 1- S' 02 NaCl 1120 (0.4 mol) (0.6 mol) (1.0 mol) (1.0 mol) A molar excess of mercaptans and caustic is employed. After cooling the reaction product mixture to about 60-70" F settling and drawing off the conversion water, the final sulfide mixture is withdrawn. The crude sulfide product is purified by distillation. The reaction is substantially quantitative and the average crude product yield is equal to 95 mol percent, based on ethyl chloride. The final mixture of diethyl sulfide and ethyl isopropyl sulfide (approximately 2 parts by volume of ethyl isopropyl sulfide to 1 part of diethyl sulfide) has a distinctive gassy odor which can be readily detected in the air when the concentration of the odorized gas is as low as 0.05% by volume. In other words, when this odorant is present in the hydrocarbon gas in proportions ranging from about 1.0 to 2.0 pounds per one million cubic feet of gas, the odor can be readily detected when as low as 0.05% by volume of the odorized hydrocarbon gas is present in the air of the room. Thus, the odor of the new warning agent present in the hydrocarbon gas is readily and unmistakably perceptible before an explosive mixture or asphyxiative concentration of the gas in the air is produced because of a leak. At the same time, the odor of the new odorant is far less objectionable to the customer than the offensive garlicky odor of the mercaptan-type odorant, although it is characteristically tgassy, more like the odor of manufactured gas. The invention thus provides a combustible hydrocarbon gas suitable as a fuel for heating, illuminating and cooking uses and at the same time characterized by a greater margm of safety, owing to the presence of a readily perceptible odorant which does not impart undesirable properties to this gas.

All of the mixed dialkyl sulfides suitable as warning agents in accordance with the present invention are liquids at room temperature. Consequently, under practically all conditions which may be encountered in the actual practice, mixed dialkyl sulfide odorants remain liquid and can be handled in accordance with the conventional practices of the art.

Furthermore, because of the relatively high volatility of dialkyl sulfide mixtures of the invention, a much higher quantity of the warning odorant can be evaporated in the hydrocarbon gas, as compared with most of the known gas odorants. For instance, as much as 18 to 19 pounds of diethyl sulfide-ethyl isopropyl sulfide mixture (boiling from about 170 to about 250 F.; ASTM-D-2l6) can be uniformly distributed by evaporation in the hydrocarbon gas held under a pressure of 1000 p. s. i. g. and at a temperature of 0 F. As a consequence of the high volatilities of dialkyl sulfide mixtures, they will not condense and separate from the fuel gas in transmission lines, commonly operated under pressures as high as 1000 p. s. i. g., when the outside temperature decreases to as low as 0 F. This property of mixed dialkyl sulfide odorants is definitely an advantage when compared to some odorants, known to liquefy and drop out at low temperatures and high pressures from the fuel gas in the lines, rendering the initial odorization ineffective.

As mentioned hereinbefore, the odor of mixed dialkyl sulfides is clearly perceptible when the odorant of the invention is present in the combustible hydrocarbon gas in proportions above about 1.0 pound per one million cubic feet of the gas and when as little as 0.05% by volume of this gas is present in the air of the room. However, the preferred concentration of the new odorant, when used in distributing combustible hydrocarbon gases for cooking, heating and illuminating purposes are comprised in the range from 0.75 to 2.0 pounds per one million cubic feet of the hydrocarbon gas, although, if desired, and particularly when the gas containing the odorant is to be transported over long distances, a larger quantity of the odorant (a higher odorization rate) may be employed.

In another representative example, the warning agent of the present invention is prepared by dissolving a mixture of n-propyl mercaptan and ethyl mercaptan (in a volume ratio of 2 parts of n-propyl mercaptan to 1 part of ethyl mercaptan) in a 20% solution of NaOH and reacting the solution with ethyl chloride, under substantially the same conditions as described hereinbefore for the preparation of diethyl sulfide-ethyl isopropyl sulfide odorant mixture. The yields of diethyl sulfide-n-propyl ethyl sulfide mixture are again in excess of mol percent, based on ethyl chloride, and the odorant properties of this sulfide mixture are highly satisfactory and similar to those of the previously described diethyl sulfide-ethyl isopropyl sulfide product.

Likewise, in another similar preparation, a 50:50 (percent by volume) mixture of n-propyl mercaptan and isopropyl mercaptan is charged into the reaction vessel containing a 20% solution of caustic together with sufficient ethyl mercaptan to obtain a volume ratio of one part ethyl mercaptan to two parts of total C -mercaptans, and upon heating ethyl chloride is introduced into the vessel for the reaction with the mercaptides formed in the solution to give a mixture of diethyl sulfide and of two ethyl propyl sulfides. Upon recovery and purification of this mixture, its odorant characteristics are found to compare favorably with those of the aforementioned effective diethyl sulfideethyl isopropyl sulfide odorant mixture.

A certain percentage of the initial mercaptan reagent (or reagents) may be permitted to remain in the mixed dialkyl monosulfide product. In fact, it has been observed in the case of the aforedescribed representative preparations that the presence of ethyl and/ or propyl mercaptans in amounts up to 10% by volume tends to improve the effectiveness of the final sulfide mixture as a warning agent when this mixture is employed to odorize combustible hydrocarbon gases. A mercaptan content up to 5% by T volume markedlyimproifes the odbr poten'c'y f mercaptan component: need ll'Otf' consist; of C -C aliphatic mercaptans. remaining in the mixture of sulfidesas aconsequence ofthepar'ticular preferred mode of its pre aration, but any one of' the Ci-C aliphatib mercaptans', or a mixture of them, may be-adde'd -to a Ci-Q dialkyl sulfide product mixture in proportions-non exceeding and preferably uprto 2% by-volume. C 6 aliphatic mercaptans. in proportions from 0.5 (015.0%: byzvolumes-are found to be entirely satisfactory for practical purposes.

The odor characteristics of the new warning agents of this invention are highly satisfactory. All of them possess a specific, though not obnoxious gassy odor, as contrasted with the well-known unpleasant garlicky and/0r oniony odor of the low molecular weight aliphatic mercaptans.

The presence of mercaptan component in amount up to 10% by volume, as described hereinabove, does not interfere with the gassy character of the dialkyl sulfide mixture and does not impose an undesirable mercaptan smell onto the olfactory sensation of a user or an observer exposed to the atmosphere contaminated by the leaking hydrocarbon fuel gas containing the sulfide odorant.

The mixed dialkyl sulfide odorants of this invention exert a clearly perceptible impact upon the olfactory sense of an unsuspecting observer at a threshold concentration of the odorized gas in the air equal to 0.05% by volume. In other words, whenever the gas containing as low as 0.5 pound of the odorant per one million cubic feet has reached a concentration of 0.05% by volume in the air in a corresponding room, compartment or working space, an average person readily becomes cognizant of the leakage, even though very small, of the odorized gas.

Insofar as the odor intensity is concerned, the new odorants of this invention are equal or often better than the cyclic sulfide odorant. Compared with the mercaptan odorants, they have an equal or better threshold odor level. This means that the concentration in the gas at which the change from the original ambient odor is first observed is either equal or lower than the corresponding concentration of a mercaptan odor. Also, their odor is more persistent than that of mercaptan odorants.

The odor intensity of the warning agents of this invention is very good. For instance, a mixture of diethyl sulfide-ethyl isopropyl sulfide (in 1:2 volume ratio and containing about 2% by volume of C -C aliphatic mercaptans), at a concentration of 1 pound per one million cubic feet of fuel gas, is about equivalent in odor intensity to 12-13 pounds per one million cubic feet of a cyclic sulfidebased commercial odorant. The odor of dialkyl sulfide mixtures is persistent and increases in intensity with time as the gas continues to leak into the room, particularly whenever the dialkyl sulfide mixture contains up to 2% by volume of C -C aliphatic mercaptans. In fact, the odor intensity of these odorant mixtures is better than that of an individual alkyl sulfide, e. g., diisopropyl sulfide, even though the latter contains up to 2% of a C -C aliphatic mercaptan. The new odorants are thermally stable. In a conventional stability test, 96% of dialkyl monosulfides remained undecomposed after the aforedescribed representative odorant mixture of diethyl sulfide and ethyl isopropyl sulfide containing up to 2% by volume of C -C aliphatic mercaptans was passed over fine copper turnings heated to 800 F. It is also resistant to oxidation by the oxygen of the air and by contact with iron oxide, so that the odor-fading is substantially non-existent.

Corrosivity of the new warning agents, i. e., their tendency to corrode iron or brass equipment, is practically nil. In areas exposed to open flame, corrosion of copper parts is but very slight.

When tested for toxicity, using laboratory mice, the new warning agents of the invention were found to be no more toxic than white unleaded gasoline, and thus require no special precautions. They do not irritate the skin or the-respiratorymenibranes. A siight irritatiomofithe eyes may be felt at the time of actual:contact butfasssoonaas the. person: exposed leaves the atmosphere: contaminated by the fuel gas containing the odorant,. the inflammation disappears without leaving. any permanent; injury;

Sulfur contribution of the new mixed: alkyl" sulfide odorants at 1 pound per one million cubic feet. concentration in the combustible hydrocarbon gas is of-th e order of 0.15 to 0.35 grain per 100 cubic. feet-.of the airvinthe room where the gas'isburnt. t I

In a closed room test, combustiblehydrocarbon gas was odorized with a representative warning agent of the invention, namely, a mixture of diethyl sulfide and ethyl isopropyl sulfide in a volume ratio of approximately 1:2 and containing 1.4% of C -C mercaptan, at an odorization rate of about 1.5 pounds per one million cubic feet of the gas. The odorized gas was transported through a pipe line a distance of 10 miles at 650 p. s. i. g. pressure. Thereupon the gas was allowed to escape into a closed room of approximately 1225 cubic feet in content at such a rate that 1.0% gas concentration would be reached in approximately 12 minutes. A number of observers (7) were employed. All of them detected the gassy odor within 1 to 2 minutes after starting the test. On continuing the admission of the gas for an additional period of 12 minutes, at which time the 1.0% gas concentration was reached, no olfactory fatigue was noted by any of the observers.

Evidently, combustible hydrocarbon gases odorized with mixed dialkyl monosulfide warning agents of the present invention possess a superior margin of safety over similar gases odorized with other known odorants of the trade, because of the unexpected high odor intensity of the new warning agents. The specific character of the sulfide mixture in these agents obviates the occurrence of olfactory fatigue and thus commends their employment in hydrocarbon fuel gases likely to form explosive mixtures with air u-pon leakage. Natural gas odorized with the warning agent of the present invention, the odor of which resembles the odor of manufactured gas, is more satisfactory to its users than natural gas odorized with low molecular weight aliphatic mercaptans. As pointed out in the aforegiven description, even the slightest leak of gas into a room can be detected long before an explosive quantity of the gas is accumulated due to a leak in the equipment or to an inadvertently left open gas-cock.

I claim:

1. A warning agent suitable for odorization of gaseous hydrocarbon fuels, said agent comprising a mixture of diethyl sulfide and an ethyl propyl sulfide, one of said two sulfides being present in an amount equal from at least 10% up to as high as by volume and the other sulfide forming the remainder to make-up by volume of said sulfide mixture.

2. A warning agent, as defined in claim 1, wherein said ethyl propyl sulfide is ethyl isopropyl sulfide.

3. A warning agent, as defined in claim 1, wherein said ethyl propyl sulfide is ethyl, normal propyl sulfide.

4. A warning agent, as defined in claim 1, said agent having in addition from 0.5 up to 10% by volume of warning agent of C -C aliphatic mercaptans.

5. A warning agent, as defined in claim 1, said agent having in addition from 0.5 up to 5% by volume of said warning agent of C -C aliphatic mercaptans.

6. Process for the odorization of a hydrocarbon fuel gas which comprises incorporating in said gas from about 0.5 to 2.0 pounds per one million cubic feet of said gas of a' warning agent mixture comprising diethyl sulfide and an ethyl propyl sulfide, from about 10 to 90% by volume of this mixture being diethyl sulfide and the remainder being the ethyl propyl sulfide.

7. Process according to claim -'6 in which the warning agent mixture has in addition a small amount not exceeding 10% by volume of C -C aliphatic mercaptans.

to' 2.0 pounds per one million cubic feet of said gas of I i l t; w Agents for Gases, Bureau llhyl p py Sulfide Volume ratio from 1 t6 2, by the Am. Gas Assoc. 420 Lexington Ave., New York, and a small amount not exceeding 10% by volume of m N,Y said mixture of C -C aliphatic mercaptans.

7 "r :8. *Process according to claim 6 in which the ethyl References Cited in the file of this patent propyl sulfide is ethyl isopropyl sulfide. UNITED STATES PATENTS ".19. Process according to claim 6 in which the ethyl Y propyl' sulfide is ethyl normal propyl sulfide. 23290555 July 1942 10. Process for the odorization of a hydrocarbon fuel 5 3-3 9 G111 19-47 gas which comprises incorporating in said gas about 0.5 OTHER REFERENCES n agent mixture comprising diethyl sulfide of Mines Monograph 4 1931 pages 17-19. Published 

1. A WARNING AGENT SUITABLE FOR ODORIZATION OF GASEOUS HYDROCARBON FUELS, SAID AGENT COMPRISING A MIXTURE OF DIETHYL SULFIDE AND AN ETHYL PROPYL SULFIDE, ONE OF SAID TWO SULFIDES BEING PRESENT IN AN AMOUNT EQUAL FROM AT LEAST 10% UP TO AS HIGH AS 90% BY VOLUME AND THE OTHER SULFIDE FORMING THE REMAINDER TO MAKE UP TO 100% BY VOLUMES OF SAID SULFIDE MIXTURE.
 6. PROCESS FOR THE ODORIZATION OF A HYDROCARBON FUEL GAS WHICH COMPRISES INCORPORATING IN SAID GAS FROM ABOUT 0.5 TO 2.0 POUNDS PER ONE MILLION CUBIC FEET OF SAID GAS OF A WARNING AGENT MIXTURE COMPRISING DIETHYL SULFIDE AND AN ETHYL PROPYL SULFIDE, FROM ABOUT 10 TO 90% BY VOLUME OF THIS MIXTURE BEING DIETHYL SULFIDE AND THE REMAINDER BEING THE ETHYL PROPYL SULFIDE. 